In many businesses and industries, hoses, fluid lines, duct pipes, tubes, conduits, manifolds and the like (hereinafter generically referred to as hoses) are used to carry liquids. After a specific use, it may be necessary to clean the hose. For example, hoses are used to carry paint to a spray gun. When painting is finished or when a new color paint is to be applied, it is necessary to clean all of the old paint from the hose. If residual paint is left in the hose, it may harden and eventually clog the hose. Or, if a different color paint is applied, any remaining old color paint may initially contaminate the new color paint. In another application, hoses used for carrying milk, for example, at a farm or at a milk processing plant, also must be frequently cleaned. If residual milk is left in the hose, it may spoil and contaminate milk subsequently carried through the hose.
Various techniques have been used for cleaning hoses. Often, as much liquid as possible initially may be purged from the hose with compressed air. In a painting system, the purged paint may be reclaimed for future use. A suitable solvent or cleaning solution is passed through the hose and finally the hose may be purged of solvent with a flow of compressed air. For milk, a soapy water solution may be passed through the hose, followed by clean water and air. For solvent-based paints, a paint solvent must be used, followed by air to dry the hose. It is known in the art that the cleaning efficiency may be improved by alternately pulsing solvent and compressed air through a hose to increase the scrubbing action. However, considerable quantities of solvent and an undesirable long time may be required to clean a paint hose.
In one improved system, solvent and compressed air have been mixed to produce a turbulent flow for cleaning a hose. The solvent and the compressed air are supplied through separate needle valves. Typically, the mixture is passed through a transparent hose and the valves are adjusted to visibly produce a desired turbulent mixture. However, solvent pressure may vary considerably in a commercial system. If, for example, several paint lines happen to be cleaned at the same time from a single solvent source, there may be significant solvent pressure variations. This will result in an improper solvent to air ratio and less than maximum turbulence in the solvent. If the hose is cleaned for a fixed time interval in an automated system, a solvent pressure change which reduces turbulence in the solvent may result in inadequate cleaning of the paint line.
It is desirable to reduce the quantity of solvent and the time required to clean a hose. Solvent is expensive to purchase and used solvent is expensive to dispose of since it is considered a hazardous waste. Further, in certain manufacturing businesses, such as in automobile body manufacturing, it is necessary to change paint color from workpiece to workpiece. Any reduction in the color changeover time may result in increased production and decreased manufacturing costs. The color change time generally is limited by the time required to clean the paint hoses.